Fibers come into play in a ramp-like pattern. Easy actions recruit slow-twitch fibers for endurance. Think walking or writing. Heavy or fast actions recruit both slow-twitch and fast-twitch muscle fibers. Think sprinting or lifting. When a set lasts longer, say 12 reps versus 6, this process just takes a bit longer. If you move as fast as possible when the reps grow difficult, this creates tension in the fast-twitch muscle fibers, even with lighter weights. High reps can work just as well for building strength and size in most cases.
Unfortunately, lactic acid builds up during the set. This gets in the way of the sites that create tension. Endurance, in one form, comes from the adaptations that take place to tolerate this better. For someone focusing on strength and size, they want to minimize this competing fatigue. This gives a reason why some choose to avoid high reps and why a cap does exist.
Before you judge higher reps as inferior to lower reps, consider the legendary 20 rep squat program. Although many consider 20 far too many reps, real-world results show immense size and strength built nonetheless. This old-school program has you perform 20 reps with the heaviest weight you can handle. You pick a weight you could only achieve 8-12 times, and somehow manage to get 20. You reach this through a rest-pause style. This means you can rest as long as needed between reps. This may blunt lactic acid. Combined with progression and plenty of calories, this approach added slabs of muscle on the old-timers and helps modern trainees as well.
20 rep squats work because they require a supreme effort. Effort ranks most importantly to get strong and muscular, as long as you use almost any reasonable rep range. I have already mentioned the tendency for long-time lifters to move toward lower reps, but have certainly seen exceptions to the rule.
I consider reps above 12 and not much further than 30 as the standard for higher reps. No clear standard exists, but it does mean you have ventured well into the glycolytic system. Here are some reasons to favor higher reps.
Hard work and training. There’s no secret formula. I lift heavy, work hard, and aim to be the best.
– Ronnie Coleman
- You have some margin for error.
A twist, tweak, or jerk can prove fatal on a low rep set. Form issues can haunt you through injuries. Good form should apply to any set, but going heavy magnifies any bad effect. One false move with a heavy weight can cripple you forever. The higher force output per rep can place greater demands on the structures of the body, especially connective tissue.
This also applies to performance. If you fail due to bad mechanics when doing only 2 reps instead of 3, you lose out on 1/3 of the set’s potential. With more reps, one poor one will likely not have as great of an effect since you will have a higher strength reserve for most of the set. Consider the bench press. Some trainees make the mistake of letting the bar travel toward their feet as they press up. Going too far will end the set. With lighter weights, you can usually adjust for this error without failing the rep. With a heavy weight, going too far will make you miss, even if you had more left in you.
With heavier weights, you may also change the mechanics of the exercise entirely. For low reps, many trainees will do a good morning instead of a squat, failing to keep the chest up while bending at the knees enough. This would transfer the load throughout only the rear parts of the lower body, while also risking the lower back.
- It may suit lower body training better.
Many report better progress using higher reps for lower body exercises. This may occur due to the great capacity for endurance the legs possess, and therefore they may benefit from a higher workload compared with the upper body. This may occur due to muscle fiber type ratio or some other less clear reason. This concept has a lot of weight in training circles but does not have much research behind it.
- You may better influence secondary growth factors.
Lactic acid and volume may influence hormones. Metabolism occurring in glycolysis, which means longer duration, may create a better environment for growth. The pump and soreness that increases with higher reps may support greater growth due to more micro-tearing of the fibers. This may also lead to more blood flow to remove by-products of fatigue and deliver nutrients. You may get a surge in muscle-building hormones that only happens through higher reps.
- You adapt to multiple demands.
Low reps tend to focus solely on muscle strength and size. Higher reps stress more systems. They can make you feel out-of-breath, which improves your wind. You feel lactic acid building up, which leads to muscular endurance. Since your body adapts to lactic acid, it interferes less with the sites for contraction over time. Add weight and you will get strong and big. For someone aiming for the best results in the least time, high rep sets of the big exercises could develop a well-rounded and not just a strong trainee.
- You may remove inhibitions with heavier weights.
A minimum time frame seems necessary to recruit maximum amount of fibers. Pushing against a wall for a second or two, even with maximum effort, will fail to build much strength and size. Your body can only recruit so many fibers at once. Extending this limit may allow all the fibers to come into play since they arrive at different times as other ones fatigue. The Golgi tendon organ, a monitor located in our muscles, may prevent excessive tension with very heavy weights. Some time also allows the tissue to further warm-up, which helps performance.
Higher Reps Work
Good reasons exist for using both high and low reps. In the end, it may not matter much which direction you go. Weight and reps share a tight relationship. You usually just express the same strength level through different reps. Charts can reasonably predict your weight at certain reps, and even more so if you add a personal coefficient. For example, you may find that when you can bench press 200 for 12 reps, that you can perform 225 for 8 and vice versa.
I find my clients do best within the range they choose, as long as it does not extend too highly, such as beyond 30. Most beginners will do well with moderate ranges, such as 6-15, and can adjust in time. Going far beyond 30 reps probably focuses on muscular and cardiovascular endurance too much. You would train these qualities better through intervals.
Lower reps and higher reps can both work. You need to decide what reasons resonate with you and trust yourself. You need to add weight over time and work hard enough to stimulate growth. Within a reasonable range, you will probably find that changing the rep range is not the answer. Trainees have thrived on many rep ranges. Make sure you have an efficient training program and that you eat, sleep, and rest enough. Use whatever rep range works for you.